This application is related to claims priority from Japanese Application No. 2000-380289, filed Dec. 14, 2000.
1. Field of the Invention
The present invention relates to a display and an image displaying method, particularly relates to a display and an image displaying method wherein gradation representation is made in a subfield mode and data every line is sequentially output and displayed in each subfield.
2. Description of the Related Art
Recently, in place of a cathode ray tube (CRT) display which has been used heretofore, a flat panel display using liquid crystal and plasma which is thin and light, which has little distortion of the screen and is hardly influenced by earth magnetism is used. Particularly, a plasma display which has a large angle of visibility because of a spontaneous emission type and the large-sized panel of which can be manufactured relatively easily attracts attention as a display of a picture signal.
Generally, for a plasma display, as halftone display between emission and non-radiation is difficult, a method called a subfield mode is used to display a halftone. In the subfield mode, the gradation of the luminance of one field is represented by dividing the time length of one field into plural subfields, allocating the proper weight of emission to each subfield and controlling the emission and non-radiation of each subfield.
Currently, in an address-sustained separation method which is a mainstream out of methods of a plasma display, one subfield includes a control pulse for respectively controlling a reset period for initializing a state of a discharge cell, an address control period for controlling the lighting and unlighting of the discharge cell and a sustention period for determining the amount of emission. These control pulses are not to be shorter than predetermined time length to realize the stable control of emission.
In the address control period, as addressing is performed based upon data for controlling lighting and unlighting every line, more time is required because the number of lines is increased for a high-resolution panel. Therefore, there is a problem that the number of subfields into which one field period can be divided is limited and enough luminance is not acquired.
For example, to realize a high-definition panel the vertical resolution of which is 1000 lines using a display panel requiring 2 xcexcs. per line for address control processing, an address control period of 2 xcexcs. (=2 xcexcs.xc3x971000 lines) per subfield is required. Generally, approximately 256 gradations (8 bits) are required to display a picture signal without deteriorating it, however, to divide one field period of approximately 16.6 ms. into eight subfields, time is hardly allocated to the sustention period. There is a problem that as most of one field period is allocated to an address control period every subfield as described above, the sustention period which contributes to panel emission cannot be secured enough.
In case the number of subfields is limited, for example in case the number of subfields is limited to 6 subfields (64 gradations), enough gradation cannot be represented and it is difficult to realize a high quality display.
Further, for a problem proper to gradation display according to the subfield mode, there is pseudo contour interference which deteriorates the quality of a dynamic image. To reduce this pseudo contour interference, a method of increasing the number of subfields and controlling the distribution of emission and the centroid of emission respectively in one field is used. As the more the number of subfields is, the more controllable emission patterns are in case the number of representable gradations is the same, the effect of reducing pseudo contour interference increases. Therefore, there is a problem that in case enough subfields are not acquired, the quality of a dynamic image when it is displayed is remarkably deteriorated by this pseudo contour interference.
In a conventional type display, it is basically regarded as important that an input signal is faithfully displayed and a method of acquiring high quality in consideration of the characteristic of a human visual sense such as dither for compensating the shortage of gradations, error diffusion processing and the control of average luminance is also partly used, however, the control of the amplitude of a signal is main.
For well-known technique, in JP-A No. H11-24628, xe2x80x9cGRADATION DISPLAY METHOD OF PLASMA DISPLAY PANELxe2x80x9d, a method of reducing address control time by interlaced scanning in a subfield equivalent to a low order bit and a method of simultaneously selecting two scanning electrodes and writing in place of interlaced scanning are disclosed, however, a concrete method of generating a signal is not disclosed.
Each line of a picture signal is data sampled in a vertical direction of one screen and when sampled data is thinned out by interlaced scanning, vertical resolution is required to be reduced by half beforehand to reduce folding interference. Hereby, vertical resolution is reduced by half and an image is displayed in low resolution.
It is known that in case sampled data is thinned out without reducing vertical resolution by half beforehand, a high frequency component of a signal is converted to a low frequency by folding interference and the image quality is greatly deteriorated.
The object of the invention is to provide a display and an image displaying method wherein the amount of the information of the resolution of an displayed image is limited if necessary positively utilizing the characteristic of a human visual sense and the statistical property of a picture signal and the synthetic image quality is enhanced.
Another object of the invention is to provide a high-resolution display and an image displaying method wherein subfields of the enough number are secured by improving total address control periods which account for the time of a field and gradation representation, a measure against pseudo contour interference and further, the realization of high-luminance display are implemented.
The invention adopts the following methods to solve the above-mentioned problems.
Address control periods are reduced by simultaneously performing addressing for two lines based upon the same data in a predetermined subfield and the time is allocated to the improvement of image quality in luminance, gradation and a pseudo contour.
Addressing every line is performed in high order subfields including the most significant subfield as in prior art and simultaneous addressing for two lines based upon the same data is performed in a group of low order subfields to which relatively small weight of emission is allocated.
Further, a subfield in which addressing independent every line is performed as in prior art is provided to a part of the group of low order subfields.
Display resolution information in units of subfield is limited by dividing an input picture signal into vertical frequency components and selectively synthesizing them again.
Further, in case a subfield in which addressing is simultaneously performed for two lines based upon the same data exists, the average value for two lines of a display signal is possibly equalized to the average value for two lines of an input signal.